Method of producing la containing alloys



United States Patent O 3,304,177 METHOD OF PRODUCING La CONTAININGALLOYS Stanley T. Wlodek, Forest Park, Ohio, assignor to GeneralElectric Company. a corporation of New York No Drawing. Originalapplication Dec. 26, 1963, Ser. No. 333,619. Divided and thisapplication Nov. 12, 1964, Ser. No. 416,671

2 Claims. (Cl. 75-171) This is a division of application Serial Number333,619, file-d December 26, 1963, and assigned to the assignee of thepresent invention.

This invention relates to nickel base alloys, and more particularly, toa solid solution type nickel base alloy of improved oxidation resistanceand fabricability.

Presently available wrought nickel base alloys can be divided into twogeneral classes: Ni-Cr-Al-Ti and Ni- Cr-Fe-Mo-W. The first class ofalloys are precipitation strengthened by the formation of Ni (Al, Ti)and depend on their aluminum and chromium content for oxidationresistance. Although the Ni-Cr-Al-Ti alloys are strong below 1600 F.their mechanical properties at higher temperatures become comparable toalloys of the Ni-Cr-Fe type which are solution-strengthened by Mo and/orW. In addition, the solution-strengthened Ni-Cr-Fe type alloys cancontain larger amounts of chromium and thus are more oxidationresistant, especially at high temperatures.

A principal object of the present invention is to improve the oxidationresistance of the Ni-Cr-Fe-Mo-W type alloys.

Improved compositions of this type are critical to the construction ofimproved propulsion systems for aircraft as well as for high temperatureprocessing equipment. In such systems and equipment, the alloys aregenerally utilized in those components exposed to the highest tem-vperatures, for example, as inlet guide vanes and combustor sections injet engines, doors and fittings on furnaces, as well as catalytic traysor reaction vessels for certain chemical processes.

Because of the high chromium content of the solutionstren-gthened typealloys and the presence of silicon, alloys of such compositions exhibitrelatively good oxidation resistance for a nickel base alloy. However,still greater oxidation resistance is required for application such asin advanced gas turbine apparatus. Because of the embrittlement whichwould result from the increase of the chromium level, and theunacceptable low strength, low melting point and emhrittlement whichwould be associated with any fiurther -increases in the silicon content,it has not been possible to improve the existing degree of. oxidationresistance of solution strengthened type nickel base alloys within thepresent limits of the alloy constituents.

The above and other objects and advantages of the present invention will'be more clearly understood from the following description and exampleswhich are not meant :as limitations on the scope of the presentinvention.

Briefly, one form of the present invention involves an improvement in anickel base alloy of the solution strengthened type consistingessentially of the elements. Cr, Mo, Fe with the balance nickel andincidental impurities in which has been included from 0.05 to less than0.3 weight percent lanthanum. In a preferred form, the alloy of thepresent invention consists essentially of, by weight, 20-23% Cr, 840%Mo, 17-20% Fe, up to 2.5% Co, up to 0.15% C, up to 2% W, 0.05 to lessthan 0.3% La with the balance Ni and incidental i purities.

In another form, the present invention contemplates the provision of theabove alloy forms to which the La has been added during melting as oneof the materials Ni La, LaFe LaCo LaAl LaSi LaC and LaCu preferably NiLa in the specific form of the present invention.

Although the element lanthanum along with cerium and other rare earthelements have been added to nickel base alloys to improve mechanicalproperties such as rupture strength at high temperatures or to improveelectrical resistance characteristics, prior reports did not recognizethe different kinds of efiects which can be achieved through theinclusion of lanthanum in a solution strengthened type nickel base alloywhich does not include the elements titanium and aluminum. It has beenrecognized, unexpectedly, that with regard to oxidation resistance,there is a different kind of oxide product which results from theoxidation of a nickel base alloy precipitation hardened through Al andTi and a solution strengthened type nickel base alloy to each of whichhas been added the element lanthanum or cerium. The additionparticularly of lanthanum to the solution strengthened type Ni-Cr-Fealloys increases the rate of incorporation of chromium in the alloy intothe scale. Through this thermodynamic etfect, the amount of chromium inthe surface oxide is increased to the point that a very protective,tightly adherent scale of almost pure Cr O results. In effect, the alloyoxidizes as if it possessed a much higher chromium content than could betolerated by limits of strength and tabrica bility. However, the extentto which this thermodynamic effect can be used is limited based on :fabricability.

In order to more fully understand this effect, two alloys which aretypical of the two classes of nickel base alloys discussed were modifiedby additions of both Ce and La. The following Table I gives thecomposition of these two alloys in the unmodified form. Alloy A istypical of the precipitation hardened type including the elements Ti andAl whereas Alloy B is typical of the solution strengthened type notincluding Al and Ti.

IMPURITIES [Percent by weight] Alloy A Examples of Alloys A and B alongwith their modifications including La and Ce were exposed at 1800 F. and

the resultant weight-gain was determined. These data are given in thefollowing Table 11 along with the condition or type of surface oxidecoating which resulted from the oxidation test.

TABLE IL-OXIDATION TESTS AT 1800 F.

Table II shows the different kind of efiect resulting from the additionof Ce and La to the two classes of nickel base alloys discussed. Inaddition, it is to be noted that the addition of Ce to Alloy R resultsin a spalled coating whereas the addition of La to Alloy A results in avery adherent type of coating. This shows that a different type ofmechanism exists with regard to the reaction of these two rare earthelements on precipitation hardening nickel base alloys. On the otherhand, the addition of Ce and La to Alloy B results in a very adherentcoating. The oxidation resistance of La additions, however, areunexpectedly greater than those resulting from the addition of Ce.

Although the oxidation resistance of Alloy B was generally improved byadditions up to 0.5 weight percent La, the fabrica-bility of the alloywas different for varying amounts of La. For example, Alloy B wasmodified with additions of 0.05, 0.07, 0.15 and 0.3 weight percentadditions of La. It was found that Alloy B including 0.3 weight percentaddition of La was not fabricable whereas the other modifications wereeven more fabricable than the unmodified alloy. These modificationswithin the range of 0.05 to less than 0.3 weight percent lanthanum werecold rolled at a reduction of about per pass whereas Alloy B itself andAlloy B modified With 0.3 weight percent La could not be readily coldrolled. Thus the improvement in iabricability which might have beengenerally concluded from prior references is not generally applicablethroughout the range of additions of La to nickel base alloys.

In order to more fully study the mechanical properties of the alloy ofthe present invention, two 15 pound heats were vacuum melted and reducedto 0.060 inch sheet without difiiculty. During initial melting trials itwas found that preparation of these alloys through the addition ofelemental lanthanum does not result in the retention of any appreciablelanthanum. Lanthanum (MP. 1688 F. density 0.224 l'bs./in. is a highlyreactive metal lighter than nickel (M.P. 2647 F., density 0.322 lbs/in?)and with a much lower melting point.

However, it was found that the high melting point and comparable densityof Ni La (M.P. 2410 F., density 0.302 l'bs./in. allows the controlledand economical alloying of lanthanum with nickel base alloys. Otherlanthanum materials having similar properties and which can be usedaccording to. the tolerance of the alloy composition being melted to allLa to the alloy are LaFe Lac-o LaAl LaSi LaC and LaCu During the meltingof the alloy of the present invention, 0.15 weight percent La was addedas Ni La. The resulting composition was, by weight, 22.1% Cr, 18.2% Fe,9.9% M0, 1.2% W, 0.8% Si, 0.15% C, 0.067% La with the balanceessentially nickel and impurities. This indicates a La recovery. Therest of the vacuum melting procedure was that used in standard practice;namely, pumping down to produce a vacuum, melting the base or base and 4major addition (e.g.: Ni or Ni and Cr); carbon de-oxidatio-n ifnecessary; addition of. minor alloying elements; homogenization; thenaddition of La material at least 5-10 minutes before pouring.

A comparison of the oxidation resistance between this particular form ofthe present invention and Alloy B are shown in the following Table 'IH.

TABLE III.400 HR. OXIDATION COMPARISON Internal Oxidation Depth(mils/side) Temp, F.

Present Invention Alloy B The following mechanical properties are thoseof the above identified specific form of the alloy of the presentinvention.

TABLE IV.MECHANIOAL PROPERTIES TENSILE [Solutioned 15 min. at 2175" F.aged 48 hrs. at 1400" F.]

Temp. C F.) UTS (K s.i.) 0.2% YS (Ksi) Percent El (KL/H1.)

Room 138 108 10. 2 G6 58 46. 5 35 29 40. 4 13 63. 5

STRESS RUPTURE Temp. F Stress (K s.i.) Life (hrs) Percent El (rm/1n.)

Thus the addition of the element lanthanum within the range of 0.05 toless than 0.3 weight percent and preferably by the new method of addingLa as Ni La, results in a diiierent kind of oxidation improvingmechanism and different eliect on fabricability within the solutionstrengthened type of nickel base alloys and between percipitationstrengthened nickel base alloys and solution strengthened nickel basealloys.

Although the present invention has been described in connection withspecific examples, it will be understood by those skilled in the art thevariations and modifications of which the present invention is capable.For example, it will be understood that the addition of La may carrysome Ce because of their occurrence in nature and the productionpracticality of making less costly types of additions. However since thepresence of Ce will reduce the amount of the preferred La addition whichcan be added without incurring deleterious effects on fabricability, thepresence of Ce and other rare earths in such commercial :alloy additionsas Mischmetal is deleterious to the maximum properties of the alloy.

What is claimed is: V

1. In a method of making an alloy including a base and alloying elementsone of which is the element La, the steps of:

heating to melt the base and alloying elements except 5 6 intermixingwith the heated melt a Labearing material References Cited by theExaminer selected from the group of materials consisting of FOREIGNPATENTS N' L F L LaAl L d L d gl a a005, aslz an along an 708,820 5/1954Great Britain. casting the melt to make the alloy. 5

ID L. P E m 2. The method of claim 1 in which the base in nickel DAVRECK: rlmary mgr and the La-bearing material is Ni La. DEAN, AssistantExammer-

1. IN A METHOD OF MAKING AN ALLOY INCLUDING A BASE AND ALLOYING ELEMENTSONE OF WHICH IS THE ELEMENT LA, THE STEPS OF: HEATING TO MELT THE BASEAND ALLOYING ELEMENTS EXCEPT LA; INTERMIXING WITH THE HEATED MELT ALA-BEARING MATERIAL SELECTED FROM THE GROUP OF MATERIALS CONSISTING OFNI5LA, LAFE5, LACO5, LAA12, LASI2 AND LACU6; AND THEN CASTING THE MELTTO MAKE THE ALLOY.
 2. THE METHOD OF CLAIM 1 IN WHICH THE BASE IN NICKELAND THE LA-BEARING MATERIAL IS NI5LA.